The present invention relates to a voltage non-linear resistor unit and an arrester unit used for a power system equipment.
In general, various resistors are used for a power system equipment. For example, a voltage non-linear resistor is used for an arrester used in an electric circuit which protects a power system from an abnormal voltage. A zinc oxide (ZnO)-based material, which is a ceramic material, is used as a base element of the voltage non-linear resistor. More specifically, a sintered body is used as the base element, which is prepared in the manner that, to the zinc oxide (ZnO) used as a main component, there are added an oxide such as bismuth (Bi), antimony (Sb), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), silicon (Si) or the like used as a secondary component, water and an organic binder added, and then, these components are sufficiently agitated. Thereafter, these components are granulated and molded by using a spray dryer or the like, and then, are sintered.
Moreover, a side of the sintered body is formed with a high resistance layer as occasion demands by applying and re-sintering a high resistance substance for preventing a creepage flash fault. Both ends of the sintered body are polished and are attached with an electrode film, and thus, a voltage non-linear resistor is manufactured. An arrester is constructed in a manner that one or plural voltage non-linear resistor elements are laminated or stacked, and then, are attached with a terminal metal fitting through an insulator. Moreover, in the arrester, a spring structure is employed for electrically connecting the terminal metal fitting.
As described above, since the spring structure is used in the arrester, the number of components is increased and a cost becomes high. In recent years, a power system equipment has been made into a small size in order to reduce a transmission cost, and it has been required to make small a structure of locating an insulator.
As prior art, in Japanese Patent Laid-Open Publication No. HEI 10-270214 and in Japanese Patent Laid-Open Publication No. HEI 10-275737, a plurality of zinc oxide sintering bodies are joined with each other by using a conductive material, and then, both end portions of the element joined are subjected to metalizing treatment, and further, is joined with a terminal metal fitting by a metallic material having a low melting point so that the element and the terminal metal fitting are formed as a unit. According to such process, there has been developed a voltage non-linear resistor unit which can reduce the number of components and can achieve a cost reduction.
However, in this type of voltage non-linear resistor unit, in the case where a junction between the voltage non-linear resistors and a junction between each voltage non-linear resistor and the terminal metal fitting is unsuitable, a uniform conductivity is hard to be obtainable. In other words, it is required that the junctions between the voltage non-linear resistors and between each voltage non-linear resistor and the terminal metal fitting are firmly made without losing a conductivity.
According to the conventional joining method, a conductive paste consisting of silver powder, glass powder and an organic binder is used as a conductive material, and glass powder contributing to a bonding strength is an insulator. The thus formed junction surface is inferior in a conductivity, and therefore, a uniform conductivity is hard to be obtainable. As a result, the following problem has arisen. That is, a current concentration is easy to be generated in discharge withstand current rating, and then, the discharge withstand current rating is decreased.
An object of the present invention is to provide a voltage non-linear resistor unit which can achieve a small size without lowering discharge withstand current rating.
Another object of the present invention is to provide an arrester unit provided with the voltage non-linear resistor unit of the character mentioned above.
These and other objects can be achieved according to the present invention by providing, in one aspect, a voltage non-linear resistor unit comprising:
at least one of voltage non-linear resistors which is composed of a columnar sintered body formed by molding and sintering a raw material, the sintered body having both end surfaces having a surface roughness in term of arithmetic average surface roughness (center line average surface roughness) Ra of 1 to 2 xcexcm and being formed with an electrode film layer;
a terminal metal fitting formed in a predetermined shape and attached to the voltage non-linear resistor; and
a soldering material arranged between the voltage non-linear resistors and between joint surfaces of the voltage non-linear resistor and the terminal metal fitting, the joint surfaces being joined by heating the soldering material and applying a load vertically to the joint surfaces while giving a rotation motion thereto.
In a preferred embodiment of this aspect, in a case of joining the voltage non-linear resistors together or joining the voltage non-linear resistor and the terminal metal fitting, a shift between central axes of one and the other joint surfaces is within a range of 0.1xc3x97R5 or less where R5 is a diameter of a smaller joint surface.
The sintered body of the voltage non-linear resistor is provided with a side surface to which an inorganic insulation coating material, which is formed with a high resistance layer containing mullite (Al6Si2O13) as a main component and including AlPO4 of 5.0 to 20 wt %, TiO2 or Fe2O3 of 0.2 to 5 wt %, is preliminarily formed. A non-crystal high resistance layer including SiO2 and Al2O3 as main component is further formed on the inorganic insulating coating material.
The electrode film formed on the sintered body is an electrode film composed of a plurality of layers comprising a first layer of Al or Al alloy and a second layer of Cu or Cu alloy.
The electrode film has a thickness of 300 xcexcm or less. The soldering material contains Sn as a main component and contains at least one of Cu, Ag and Sb as a secondary component such that Sn is contained by 70 to 99%, Ag is contained by 3 to 20%, and Cu and Sb are contained by 5% or less.
In another aspect of the present invention, there is provided an arrester unit comprising:
a voltage non-linear resistor unit comprising at least one of voltage non-linear resistors which is composed of a columnar sintered body formed by molding and sintering a raw material, the sintered body having both end surfaces having a surface roughness in term of arithmetic average surface roughness Ra of 1 to 2 xcexcm and being formed with an electrode film layer, a terminal metal fitting formed in a predetermined shape and attached to the voltage non-linear resistor, and a soldering material arranged between the voltage non-linear resistors and between joint surfaces of the voltage non-linear resistor and the terminal metal fitting, the joint surfaces being joined by heating the soldering material and applying a load vertically to the joint surfaces while giving a rotation motion thereto;
a thermosetting perforated insulating tube which covers portions of the voltage non-linear resistor unit except the terminal metal fitting of both end portions of the voltage non-linear resistor unit;
a metallic disc arranged in the terminal metal fitting of the voltage non-linear resistor unit so as to hold an end portion of the perforated insulating tube;
another terminal metal fitting provided through the metallic disc and engaged with a projected screw portion which has a disc-shaped surface joined with the voltage non-linear resistor and has a diameter of ⅓ of or more than a diameter of the first-mentioned terminal metal fitting formed on the joint surface side at the central portion of the first-mentioned terminal metal fitting; and
an elastic insulation cover member covering an outer periphery of the perforated insulating tube.
In this aspect, the metallic disc includes a plurality of protrusions at a side facing the first-mentioned terminal metal fitting of the voltage non-linear resistor unit. The elastic insulating cover member is formed with a thin wall portion in one directional side.
According to the present invention of the structures and characters mentioned above, a clearance between the voltage non-linear resistors forming the electrode film and a clearance between both the end surfaces of the voltage non-linear resistor and the terminal metal fitting are joined by means of soldering material. Therefore, it is possible to provide a voltage non-linear resistor unit which has a compact size with reduced cost. Furthermore, since the bonding strength of the voltage non-linear resistors is high, it is possible to provide a voltage non-linear resistor unit with no peeling even if it receives an external force, an ambient temperature, and an internal heating effect.
Furthermore, these voltage non-linear resistor units are fully joined in its structure, and in the manufacturing of an arrester unit, in the case of covering these voltage non-linear resistor units with the perforated insulating tube and the elastic insulating cover member, these members are not held between the joint interfaces. Therefore, it is possible to prevent a corona generated in a voltage application without losing an electrical characteristic.